The present invention is related to a semiconductor device.
A semiconductor device has an insulating substrate with semiconductor chips mounted thereon and the insulating substrate is joined to the surface of a heat radiating plate. In such a semiconductor device, heat generated by the semiconductor chips is released to the heat radiating plate through the insulating substrate. However, the difference in coefficient of thermal expansion between the insulating substrate and the heat radiating plate may cause the heat radiating plate to be warped. Japanese Patent Application Publication 2000-332170 discloses a semiconductor device to solve the problem. The semiconductor device of the Publication has an insulating substrate with semiconductor chips mounted on one surface thereof and a copper plate joined to the other surface thereof by soldering.
The surface of the copper plate that is opposite from the insulating substrate is joined by soldering to an auxiliary sheet (e.g., a molybdenum sheet) having a coefficient of thermal expansion substantially equivalent to that of the insulating substrate. This structure keeps balance between different stresses generated on opposite surfaces of the copper plate due to the thermal change thereby to prevent the copper plate from being warped.
Though the molybdenum sheet as the auxiliary sheet may be joined to the copper plate as the heat sink by soldering, it is not easy to join these two different sheets by aluminum brazing. The joint made by the soldering is low in strength and reliability.
The present invention is directed to providing a reliable semiconductor device in which an anti-warping sheet can be joined to a heat sink easily by brazing for preventing the heat sink from being warped.